Endogenous pacemakers and exogenous zeitgebers

Question 1

What is an endogenous pacemaker?

Answer 1

An internal body clock

Question 2

What is an exogenous zeitgeber?

Answer 2

External changes to the environment

Question 3

What is the suprachiasmatic nucleus (SCN)?

Answer 3

A tiny bundle of nerve cells located in the hypothalamus. It is one of the primary endogenous pacemakers in mammalian species and it is influential in maintaining circadian rhythms

Question 4

How does the SCN work?

Answer 4

Receives light from the optic chiasm which continues when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight while we are asleep

Question 5

What does evidence from Moore and Eichler (1972) and Stephan and Zucker (1972) demonstrate?

Answer 5

Selective damage to SCN abolished circadian rhythms in rats.

Question 6

Summarise Ralph et al (1990)

Answer 6

Bred ‘mutant’ hamsters who have a 20h rather than 24h circadian rhythm. When they transplanted the SCN from immature mutant hamsters into adult hamsters whose SCN had previously been removed, they found they regained their circadian rhythms but had a cycle length of 20h rather than 24h. This shows that 20h cycle was imposed on the adult hamsters.

Question 7

Summarise Decoursey et al (2000)

Answer 7

Destroyed the SCN connections in the brains of 30 chipmunks who were returned to their natural habitat and observed for 80 days. The sleep/wake cycle of the chipmunks disappeared and by the end of the observation period most had been killed by predators.

Question 8

Why is light a key exogenous zeitgeber?

Answer 8

It can reset the SCN, playing a role in the sleep/wake cycle.
Has an indirect influence on key processes in the body such as the functioning of hormones and circulation

Question 9

Summarise Campbell and Murphy (1998)

Answer 9

Demonstrated that light may be detected by skin receptor sights on the body even when the same information is not detected by the eyes.
15 participants woken at various points in the night, light pad shone on back of their knees. This altered some of their sleep/wake cycles by up to 3 hours

Question 10

Why may the role of exogenous zeitgebers be over exaggerated?

Answer 10

Those who live in artic regions where the sun doesn’t set in summer months show normal sleeping patterns despite prolonged exposure to light.

Question 11

What age in infants are circadian rhythms typically entrained?

Answer 11

16 weeks

Question 12

What has research suggested about overcoming jet lag?

Answer 12

Adapting to local times of eating and sleeping rather than responding to your own fatigue and hunger is more effective